1. The field of art to which the invention pertains includes the art of pressure reducing fluid flow devices and noise attenuation therefor.
2. For a variety of purposes, it is desirable and/or necessary in fluid transmission systems to effect high pressure drops at some predetermined location in the flow conduit. Typically, the pressure drop is effected by use of a pressure reducing valve or some other commercially available device such as those providing an elongated tortuous flow path of a type disclosed, for example, in U.S. Pat. No. 3,434,500 or a turning pattern as disclosed, for example, in U.S. Pat. No. 3,514,074. In the absence of sound attenuation equipment operably associated with such devices, the attendant noise level with large pressure reductions can reasonably be expected to be on the order of about 120 dbA and above in the course of a 3000 psig. drop. When occurring in a remote or isolated location, noise levels of that magnitude can readily be tolerated, but where occurring in a work area within hearing distance of working personnel, such noise levels can prove to be most annoying and objectionable. Moreover, with the advent of Federal OSHA (Occupational Safety and Hazards Administration) standards, it is now required as a matter of law that noise levels in working areas be maintained at or below 90 dBA when occurring for durations of eight hours per day. This prescribed level is reasonably expected to be reduced at some future date.
Typical prior art for fluid flow pressure reduction with noise attenuation is disclosed, for example, in U.S. Pat. No. 3,447,556. Commercial devices for noise attenuation are likewise available such as the Cavitation Control Trim Mark One and Dragon Tooth valve trim manufactured by Valtek, Inc. of Provo, Utah; Whisper Trim.RTM. and Cavitrol.RTM. valve cages manufactured by Fisher Controls, Marshalltown, Iowa; Lo-dB control valve labyrinth trim manufactured by Masoneilan International, Norwood, Mass.; Self "Drag" valves manufactured by Control Components, Inc., Irvine, Calif., CTV.TM. and Flash-Flo.RTM. valve trim manufactured by Hammel Dahl/Conoflow Division of ITT of Warwick, R.I.; and Jordan sliding gate valve manufactured by the Jordan Division of Richards Industries, Inc., Cincinnati, Ohio. While these and other commercial units are known to produce varying degrees of generally satisfactory noise attenuation in such fluid reducing systems, their ultimate effectiveness in relation to their premium cost can generally be regarded as somewhat high relative to comparable valves lacking the attenuation feature. Despite recognition of the foregoing, a ready solution able to achieve increased noise attenuation has not heretofore been known.